It’s on the level

Measuring noise, part 10

(For the reason that is explained in Adding to the confusion, which was posted on 1 Nov, the bottom threshold for the yellow dot range/top threshold for the grey dot range should be 65 dBA, not 68 dBA as is stated below.)

In my last blog (4 Jul) I looked at the way that HS2 Ltd has identified properties at risk from noise annoyance from HS2 and has graded them into red, yellow and grey severities. In this current blog I will try and make some assessment of what having a coloured dot on your property might mean to you, and whether the thresholds that HS2 Ltd has employed are reasonable.

So if you are unfortunate to find that a red dot appears on the HS2 Ltd map just where your property is located, what does this mean? Well, you may recall that I asked you to remember the noise level at the end of Heathrow’s runways in my blog of 30 Jun. If you recall that level was 72 dBA, which to human hearing is imperceptible from the 73 dBA threshold value being employed by HS2 Ltd for the red dot properties. So red dot means the noise nuisance will be at least as loud as living at the end of a Heathrow runway. That’s pretty loud then; I for one would find it impossible to live with that equivalent level of noise all day.

But don’t just take my word for it. The Department for Communities and Local Government has published Planning Policy Guidance 24: Planning and Noise (available here) to guide local authorities in England on the use of their planning powers to minimise the adverse impact of noise. This document includes tables in Annex 1 which relate planning decisions to noise exposure levels. The advice of this document is that planning applications should “normally be refused” where the average daytime noise from rail traffic is greater than 74 dBA.

What about a yellow dot then; what does that mean? Remember that the yellow dot covers a range that starts at 68 dBA and goes up to the bottom of the red dot range (73 dBA). This is still pretty bad; remember that 68 dBA qualifies you for a property noise insulation grant to fit double glazing, etc. The advice of Planning Policy Guidance 24 is that planning applications should “not normally be granted” when the noise level exceeds 66 dBA. Current Government guidelines for aircraft noise regard 69 dBA as representing “high levels of significant community annoyance”. So these two sets of standards seem to agree that the yellow dot situation is pretty bad.

As I mentioned in my blog of 4 Jul, the grey dot covers a very large range; it spans from 50 dBA to where the yellow dot range starts at 68 dBA, which is nearly four times as loud to the human ear. So how can we get some feel for what the grey dot means?

The provisions of Planning Policy Guidance 24 come into play at 55 dBA, where the advice is that the planning authority should impose appropriate conditions “to ensure an adequate level of protection against noise”. So that document regards 55 dBA as the level at which noise nuisance becomes a planning factor. Current Government guidelines for aircraft noise consider that “the onset of significant community annoyance” starts at 57 dBA and that 69 dBA represents “high levels of significant community annoyance”; both of these thresholds are, of course, within the grey dot range.

The World Health Organisation (WHO) specifies guideline values for community noise for a wide range of specific environments in Table 4.1 on page 65 of its publication Guidelines for Community Noise (available here). This table sets the limit at which people become “moderately annoyed” by noise at 50 dBA and upgrades this to “serious annoyance” at 55 dBA.

So I think that the appropriate question to ask if your property is indicated by a grey dot is: “Yes, but where am I in the wide range that this indicates?”. You can ask the question, but I think that it is unlikely that you will get an answer anytime soon.

Another important point that appears to have been overlooked by HS2 Ltd is that the limits specified by both the Department for Communities and Local Government and the WHO are specifically daytime figures. Both of these authorities define lower limits for night-time noise. The WHO defines the night as an 8 hour period, without specifying the clock times. However, since HS2 Ltd has advised that the operational hours of HS2 will be 05:00 to 24:00 hrs, this must include three hours of WHO night-time. Annex 1 of Planning Policy Guidance 24: Planning and Noise defines night-time as 23:00 to 07:00, so this again covers three hours of normal HS2 operation. There may, of course be additional night-time noise nuisance from HS2 due to overnight maintenance operations.

So HS2 Ltd, where are the night-time noise assessments?


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